Press molding method and press molding apparatus

ABSTRACT

The present disclosure is applied to a press molding method for press-molding a workpiece by a press die composed of an upper die and a lower die while holding the workpiece by a die cushion. The press molding method according to the present disclosure includes pressing process, in which a press position at which the workpiece is pressed by the press die is gradually lowered while repeatedly pressing and releasing the workpiece by the press die a plurality of times until the press position reaches a bottom dead center, wherein in the pressing process, a holding force for holding the workpiece by the die cushion is controlled separately from a press molding force for press-molding the workpiece by the press die.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2017-178751, filed on Sep. 19, 2017, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a press molding method and a pressmolding apparatus.

A method of sandwiching and press-molding a metal plate, which is aworkpiece, by an upper die and a lower die in the vertical direction isoften used to mold automobile parts and the like (see, for example,Japanese Unexamined Patent Application Publication No. 2005-199318).

In the press molding method described in Japanese Unexamined PatentApplication Publication No. 2005-199318, in order to prevent the metalplate from cracking, after a punch (the lower die) is first brought intocontact with the metal plate and the molding is started, an operation oftemporarily releasing the punch from the metal plate and molding themetal plate again using the punch and a die (the upper die) is performedat least one or more times until the punch reaches an end of a strokeand the molding is completed.

In addition, in the press molding method disclosed in JapaneseUnexamined Patent Application Publication No. 2005-199318, the metalplate is molded while it is being sandwiched between a blank holder (adie cushion) and a die in order to prevent the metal plate fromwrinkling.

SUMMARY

However, the press molding method disclosed in Japanese UnexaminedPatent Application Publication 2005-199318 does not adjust a blankholding force exerted by the blank holding. Therefore, even when theworkpiece can be prevented from cracking, it may not be prevented fromwrinkling, which leads to a problem that it is not possible to bothprevent the workpiece from cracking and to prevent the workpiece fromwrinkling.

The present disclosure has been made to solve the above-mentionedproblem. The present disclosure aims to provide a press molding methodand a press molding apparatus capable of both preventing a workpiecefrom cracking and preventing the workpiece from wrinkling.

An example aspect of the present disclosure is a press molding methodfor press-molding a workpiece by a press die composed of an upper dieand a lower die while holding the workpiece by a die cushion. The pressmolding method includes pressing process, in which a press position atwhich the workpiece is pressed by the press die is gradually loweredwhile repeatedly pressing and releasing the workpiece by the press die aplurality of times until the press position reaches a bottom deadcenter. In the pressing process, a holding force for holding theworkpiece by the die cushion is controlled separately from a pressmolding force for press-molding the workpiece by the press die.

An example aspect of the present disclosure is press molding apparatusincluding a press die composed of an upper die and a lower die and a diecushion, configured to press-mold a workpiece by the press die whileholding the workpiece by the die cushion, and configured to executepressing process, in which a press position at which the workpiece ispressed by the press die is gradually lowered while repeatedly pressingand releasing the workpiece by the press die a plurality of times untilthe press position reaches a bottom dead center. The press moldingapparatus includes:

-   -   a first control unit configured to control, in the pressing        process, a press molding force for press-molding the workpiece        by the press die; and    -   a second control unit configured to control, in the pressing        process, a holding force for holding the workpiece by the die        cushion separately from the press molding force controlled by        the first control unit.

The above example aspects achieve an effect of providing a press moldingmethod and a press molding apparatus capable of both effectivelypreventing a workpiece from cracking and effectively preventing theworkpiece from wrinkling.

The above and other objects, features and advantages of the presentdisclosure will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a configuration example of a press moldingapparatus according to a first embodiment;

FIG. 2 is a view showing an example of a press molding method accordingto related art;

FIG. 3 is a view showing an example of the press molding methodaccording to the first embodiment;

FIG. 4 is a view showing an example of movements of a lower surface ofan upper die and blank holding surfaces during a molding process by thepress molding method according to the first embodiment;

FIG. 5 is a view showing an example of a stress-strain diagram estimatedfor a metal plate being molded by the press molding method according tothe first embodiment;

FIG. 6 is a view showing a configuration example of a press moldingapparatus according to a second embodiment; and

FIG. 7 is a view showing a configuration example of a press moldingapparatus according to a third embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. The same or corresponding elements aredenoted by the same signs throughout the drawings, and repeateddescriptions will be omitted as necessary for the sake of clarity.

(1) First Embodiment

First, a configuration of the press molding apparatus 1 according to afirst embodiment will be described with reference to FIG. 1. FIG. 1 is aview showing a configuration example of a press molding apparatus 1according to the first embodiment.

As shown in FIG. 1, the press molding apparatus 1 according to the firstembodiment includes an upper die 10, a lower die 20, a slide 30, a diecushion apparatus 40, a slide motion controller 50, a cushion motioncontroller 60, and a synchronization control unit 70.

In the upper die 10, a projection is formed at a center on a lowersurface side, and in the lower die 20, a recess corresponding to theprojection of the upper die 10 is formed at a center on an upper surfaceside. The upper die 10 and the lower die 20 are disposed on the upperand lower sides, respectively, in such a way that the projection of theupper die 10 and the recess of the lower die 20 face each other. Theupper die 10 and the lower die 20, which constitute a press die,sandwich a metal plate W, which is a workpiece, in a vertical directionand press-mold (draw) the metal plate W into a hat-shape.

Regarding the slide 30, the upper die 10 is fixed to a lower surfacethereof. The slide 30 is driven by a servo motor or a hydraulic servo(not shown) to be elevated or lowered. Thus, the upper die 10 iselevated or lowered together with the slide 30 while the upper die 10 isfixed to the lower surface of the slide 30. The position of the lowerdie 20 is fixed. When the slide 30 is lowered, a press molding force forpressing the metal plate W in the vertical direction is generated by theupper die 10 and the lower die 20.

The die cushion apparatus 40 is provided for the purpose of effectivelypreventing the metal plate W from wrinkling when the metal plate W isbeing press-molded. The die cushion apparatus 40 includes a die cushionmain body 41 that is driven by the servo motor or the hydraulic servo(not shown) to be elevated or lowered. The die cushion main body 41 isdisposed below the lower die 20. The die cushion apparatus 40 includesdie cushions 42 extending upward from an upper surface of the diecushion main body 41 and disposed along outer walls of the lower die 20.The recess of the lower die 20 penetrates vertically. The die cushionapparatus 40 includes a die cushion 43 extending upward from the uppersurface of the die cushion main body 41 and inserted into the recess ofthe lower die 20. When the die cushion main body 41 is elevated, aholding force (hereinafter referred to as a blank holding force) forsandwiching and holding the metal plate W in the vertical directionbetween the upper die 10 and the die cushions 42 and 43 is generated bythe die cushions 42 and 43.

During the press-molding of the metal plate W, the press molding forceis generated by the upper die 10 and the lower die 20 to press-mold themetal plate W while the blank holding force is being generated by thedie cushions 42 and 43 to hold the metal plate W.

The slide motion controller 50 is a first control unit that controls theoperation for elevating and lowering the slide 30 (the upper die 10).When the slide 30 (the upper die 10) is elevated or lowered, theposition of the lower surface of the upper die 10 changes, and the pressmolding force exerted on the metal plate W changes. Therefore, bycontrolling the operation for elevating and lowering the slide 30 (theupper die 10), it is possible to control the press molding force exertedon the metal plate W.

The cushion motion controller 60 is a second control unit that controlsthe operation for elevating and lowering the die cushion main body 41.When the die cushion main body 41 is elevated or lowered, the positionsof the upper surfaces of the die cushions 42 and 43 (i.e., the positionsof the blank holding surfaces) change, and the blank holding forceexerted on the metal plate W changes. Therefore, by controlling theoperation for elevating and lowering the die cushion main body 41, it ispossible to control the blank holding force exerted on the metal plateW.

The synchronization control unit 70 controls a timing of the operationfor elevating and lowering the die cushion main body 41 controlled bythe cushion motion controller 60 so that it is synchronized with atiming of the operation for elevating and lowering the slide 30 (theupper die 10) controlled by the slide motion controller 50. For example,the synchronization control unit 70 performs synchronization controlsuch as starting to elevate the die cushion main body 41 at the timingwhen the slide 30 (the upper die 10) starts to be lowered.

As described above, in the first embodiment, control on the pressmolding force exerted by the upper die 10 and the lower die 20, which isperformed by the slide motion controller 50, and control on the blankholding force exerted by the die cushions 42 and 43, which is performedby the cushion motion controller 60, are separately performed. However,as mentioned above, the timings of the control on the press moldingforce and the control on the blank holding force are synchronized by thesynchronization control unit 70.

Next, a press molding method according to the first embodiment will becompared with the press molding method according to the related art.

First, a press molding method according to the related art will bedescribed with reference to FIG. 2. FIG. 2 is a view showing an exampleof the press molding method according to the related art. As shown inFIG. 2, the upper die 10 is lowered from an initial position, and thepress molding force is generated by the upper die 10 and the lower die20 to press the metal plate W (processes P91, P92, and P93). At thistime, the die cushions 42 and 43 are elevated from the initial position,and the blank holding force is generated by the die cushions 42 and 43to hold the metal plate W. In this way, the metal plate W is pressed bythe upper die 10 and the lower die 20 while the metal plate W is beingheld by the die cushions 42 and 43. After that, the upper die 10 isfurther lowered so that a press position at which the metal plate W ispressed reaches a press bottom dead center (a process P94).

From the process P92 onward, the metal plate W is pressed by the upperdie 10 and the lower die 20 at all times. Thus, the amount of inflow ofthe material of the metal plate W flowing into a vertical wall part ofthe recess of the lower die 20 becomes insufficient, and the metal plateW may crack at the vertical wall part.

Next, the press molding method according to the first embodiment will bedescribed with reference to FIG. 3. FIG. 3 is a view showing an exampleof the press molding method according to the first embodiment.

As shown in FIG. 3, first processes P1 to P3 are similar to theprocesses P91 to P93 according to the related art, respectively.

However, in the subsequent process P4, the upper die 10 is elevated.Then, the pressing on the metal plate W by the upper die 10 and thelower die 20 is released, and the material of the metal plate W flowsinto the vertical wall part. This effectively prevents the metal plate Wfrom cracking at the vertical wall part.

Then, in the subsequent process P5, the upper die 10 is lowered again.Thus, the metal plate W is pressed by the upper die 10 and the lower die20. At this time, the press position at which the metal plate W ispressed is lower than the press position when the upper die 10 waslowered last time.

After that, the processes P4 and P5 are repeated until the pressposition of the metal plate W reaches the press bottom dead center(process P6).

In this way, in the first embodiment, the press position of the metalplate W is gradually lowered to the press bottom dead center while themetal plate W is repeatedly pressed and released by the upper die 10 andthe lower die 20. When the upper die 10 is lowered, the amount of inflowof the material of the metal plate W flowing into the vertical wall partof the lower die 20 becomes insufficient, and the metal plate W maycrack at the vertical wall part. However, in the first embodiment, theupper die 10 is elevated, and the material of the metal plate W is madeto flow into the vertical wall part of the lower die 20 before the metalplate W starts to crack due to the lowering of the upper die 10. Thiseffectively prevents the metal plate W from cracking at the verticalwall part.

In the first embodiment, the control on the blank holding force exertedby the die cushions 42 and 43 is performed separately from the controlon the press molding force exerted by the upper die 10 and the lower die20. Therefore, for example, in the situation where the metal plate W isless prone to wrinkling but is prone to cracking, the blank holdingforce can be reduced to increase the amount of inflow of the material ofthe metal plate W flowing into the vertical wall part of the lower die20. This more effectively prevents the metal plate W from cracking. Onthe contrary, in the situation where the metal plate W is less prone tocracking but is prone to wrinkling, the blank holding force can beincreased to effectively prevent the metal plate W from wrinkling. Thus,it is possible to both effectively prevent the metal plate W fromcracking and to effectively prevent the metal plate W from wrinkling.

Next, a method of controlling the blank holding force exerted by the diecushions 42 and 43 and the press molding force exerted by the upper die10 and the lower die 20 will be described in detail with reference toFIG. 4. FIG. 4 is a view showing an example of movement of the lowersurface of the upper die 10 and the blank holding surfaces (the uppersurfaces of the die cushions 42 and 43) while the metal plate W ismolded by the press molding method according to the first embodiment. InFIG. 4, the horizontal axis represents time [second], and the verticalaxis represents a stroke [mm] indicating a distance from the pressbottom dead center. Further, FIG. 4 shows a state in which the processesP4 and P5 of FIG. 3 are repeated.

First, a method of controlling press molding force exerted by the upperdie 10 and the lower die 20 will be described with reference to FIG. 4.As shown in FIG. 4, the upper die 10 is elevated by T1 [mm] in theprocess P4 and lowered by T2 (T2>T1) [mm] in the process P5. Thus, whenthe processes P4 and P5 are performed once, the upper die 10 is loweredby T2−T1 [mm]. By repeating these processes P4 and P5 a plurality oftimes, the upper die 10 is gradually lowered, and consequently the pressposition of the metal plate W can be gradually lowered, so that themetal plate W is gradually molded.

As described above, when the upper die 10 is lowered, the amount ofinflow of the material of the metal plate W flowing into the verticalwall part of the lower die 20 becomes insufficient, and the metal plateW may crack at the vertical wall part. However, in the first embodiment,the upper die 10 is elevated in the process P4 before the metal plate Wstarts to crack so that the material of the metal plate W flows into thevertical wall part of the lower die 20, and then the upper die 10 islowered again in the process P5. This effectively prevents the metalplate W from cracking at the vertical wall part of the lower die 20. Theeffect of preventing the metal plate W from cracking improves as theamount of molding of the metal plate W (corresponding to T2−T1) becomesfiner.

Further, since the metal plate W is gradually molded, the molding loadapplied by the upper die 10 can also be reduced. Moreover, since themetal plate W is gradually molded, it is possible to prevent spring backfrom occurring at a part of the metal plate W molded near a shoulderpart of the lower die 20. This improves accuracy fixability.

Next, the principle by which the press molding method according to thefirst embodiment can effectively prevent the crack from occurring willbe described with reference to FIG. 5. FIG. 5 is a view showing anexample of a stress-strain diagram estimated for the metal plate W inthe process of it being molded by the press molding method according tothe first embodiment. In FIG. 5, the horizontal axis represents strainε, and the vertical axis represents stress σ. In addition, X1 and X2shown in FIG. 5 represent states of the metal plate W at X1 and X2 inFIG. 4, respectively.

As shown in FIG. 5, while the state of the metal plate W is X1, when theupper die 10 is elevated in the process P4, the stress applied to themetal plate W at the vertical wall part of the lower die 20 is reduced,and a region of the vertical wall part shrinks by an amount of elasticdeformation. Then, the material of the metal plate W flows into thevertical wall part. Next, when the upper die 10 is lowered in theprocess P5, the stress applied to the metal plate W at the vertical wallpart of the lower die 20 is increased. Thus, the region of the verticalwall part extends by an amount of the elastic deformation, so that theregion of the vertical wall part plasticizes to the state of X2, inwhich the state of deformation progresses more than it is at theoriginal state of X1. In this way, every time the processes P4 and P5are repeated, the material of the metal plate W flows into the verticalwall part of the lower die 20 and the strain of the metal plate Wprogresses.

Next, a method of controlling the blank holding force exerted by the diecushions 42 and 43 will be described with reference to FIG. 4. In thefirst embodiment, the control on the blank holding force exerted by thedie cushions 42 and 43 is performed separately from the control on thepress molding force exerted by the upper die 10 and the lower die 20.FIG. 4 shows two patterns, patterns 1 and 2, regarding the method ofcontrolling the blank holding force exerted by the die cushions 42 and43.

As shown in FIG. 4, the pattern 1 is a pattern in which the metal plateW is pressed at all times by the die cushions 42 and 43 while theprocesses P4 and P5 are repeated. Specifically, the blank holdingsurfaces are moved in the same manner as that of the lower surface ofthe upper die 10 so that the distance between the blank holding surfacesand the lower surface of the upper die 10 is always constant, that is,so that the blank holding force is always constant and large. Thepattern 1 is a pattern that is used, for example, in a situation wherethe metal plate W is less prone to cracking but is prone to wrinkling.The pattern 1 can increase the blank holding force to effectivelyprevent the metal plate W from wrinkling.

On the other hand, in the pattern 2, while the processes P4 and P5 arebeing repeated, the state in which the metal plate W is pressed by thedie cushions 42 and 43 and the state in which the pressing by the diecushions 42 and 43 is released are repeated. Specifically, in theprocess P5, the distance between the blank holding surfaces and thelower surface of the upper die 10 is increased at the timing when thelowering of the upper die 10 is completed to thereby reduce the blankholding force, so that the pressing on the metal plate W by the diecushions 42 and 43 is released. Moreover, in the process P5, thedistance between the blank holding surfaces and the lower surface of theupper die 10 is reduced while the upper die 10 is being lowered tothereby increase the blank holding force, so that the die cushions 42and 43 press the metal plate W again. However, the pattern 2 is notlimited to this, and may be a pattern that reduces the blank holdingforce at all times. The pattern 2 is a pattern used, for example, in asituation where the metal plate W is less prone to wrinkling but isprone to cracking. The pattern 2 reduces the blank holding force toallow the material of the metal plate W to flow into the vertical wallpart of the lower die 20, thereby making it possible to effectivelyprevent the metal plate W from cracking.

As described above, in the first embodiment, the control on the blankholding force exerted by the die cushions 42 and 43 is performedseparately from the control on the press molding force exerted by theupper die 10 and the lower die 20. Therefore, for example, in the methodof controlling the blank holding force, the pattern 1 can be used in asituation where the metal plate W is less prone to cracking but is proneto wrinkling, while the pattern 2 can be used in a situation where themetal plate W is less prone to wrinkling but is prone to cracking. Thus,it is possible to both effectively prevent the metal plate W fromcracking and to effectively prevent the metal plate W from wrinkling.

In the pattern 2, when the pressing of the metal plate W by the diecushions 42 and 43 is released, in a predetermined number of times ofthe releasing out of a plurality of times of the releasing, the metalplate W may be in contact with both of the upper die 10 and the diecushions 42 and 43, and in a remaining number of times of the releasingout of the plurality of times of the releasing, the metal plate W may beseparated from at least one of the upper die 10 and the die cushions 42and 43. The state in which the metal plate W is in contact with both ofthe upper die 10 and the die cushions 42 and 43 and the state in whichthe metal plate W is separated from at least one of the upper die 10 andthe die cushions 42 and 43 can transition to either state, for example,by adjusting the distance between the blank holding surfaces and thelower surface of the upper die 10, namely, the blank holding force. Forexample, in a situation where the metal plate W is less prone towrinkling but is prone to cracking, control may be performed in such away that the metal plate W is separated from at least one of the upperdie 10 and the die cushions 42 and 43, and the blank holding is notperformed. Further, in a situation where the metal plate W is prone towrinkling and cracking, control may be performed in such a way that themetal plate W is in contact with both of the upper die 10 and the diecushions 42 and 43, and the blank holding is performed by a small blankholding force. Thus, it is possible to both effectively prevent themetal plate W from cracking and to effectively prevent the metal plate Wfrom wrinkling more accurately.

(2) Second Embodiment

A configuration of a press molding apparatus 2 according to a secondembodiment will be described with reference to FIG. 6. FIG. 6 is a viewshowing a configuration example of the press molding apparatus 2according to the second embodiment. As shown in FIG. 6, the pressmolding apparatus 2 according to the second embodiment differs from thepress molding apparatus 1 according to the first embodiment in that thepress molding apparatus 2 further includes a state monitoring controller80 in addition to the components included the press molding apparatus 1according to the first embodiment. The configuration of the secondembodiment other than the state monitoring controller 80 is the same asthat of the first embodiment.

The state monitoring controller 80 monitors at least one of an equipmentstate of the press molding apparatus 2 (e.g., a temperature and amolding load applied by the upper die 10), a material state of the metalplate W (e.g., the amount of inflow of the material of the metal plate Wflowing into the vertical wall part of the lower die 20), or die statesof the upper die 10 and the lower die 20 (e.g., an amount of wear of theupper die 10 and the lower die 20 and the number of shots of the upperdie 10).

For example, regarding the equipment state, the temperature can bemonitored using a temperature sensor or the like, and the load appliedto the upper die 10 can be monitored using a load sensor or the likeattached to, for example, the slide 30. Regarding the material state,the amount of inflow of the material of the metal plate W can bemonitored by, for example, detecting displacement of the metal plate Wby a laser displacement meter. Regarding the die state, the amount ofwear of the upper die 10 and the lower die 20 can be monitored by, forexample, detecting the size of the gap between the upper die 10 and thelower die 20, and the number of shots of the upper die 10 can bemonitored by, for example, measuring the number of times the upper die10 is elevated and lowered.

In the second embodiment, the slide motion controller 50 controls theoperation for elevating and lowering the slide 30 (the upper die 10),namely, the press molding force exerted on the metal plate W, based onat least one of the equipment state of the press molding apparatus 2,the material state of the metal plate W, and the die state of the upperdie 10 and the lower die 20, which have been monitored by the statemonitoring controller 80.

For example, when the slide motion controller 50 determines that theamount of inflow of the material of the metal plate W flowing into thevertical wall part of the lower die 20 is large based on the materialstate of the metal plate W, the slide motion controller 50 controls thepress molding force so that it is large. By doing so, the number oftimes the upper die 10 is elevated and lowered can be reduced, and thusthe productivity can be improved. On the contrary, when the slide motioncontroller 50 determines that the amount of inflow of the material ofthe metal plate W flowing into the vertical wall part of the lower die20 is small, the slide motion controller 50 controls the press moldingforce so that it is small. By doing so, the stress applied to the metalplate W at the vertical wall part of the lower die 20 can be reduced,thereby making it possible to effectively prevent the metal plate W fromcracking at the vertical wall part.

In addition, when the slide motion controller 50 determines that themolding load applied by the upper die 10 is small based on the equipmentstate of the press molding apparatus 2, the slide motion controller 50controls the press molding force so that it is large. By doing so, thenumber of times the upper die 10 is elevated and lowered can be reduced,and thus the productivity can be improved. On the contrary, when theslide motion controller 50 determines that the molding load applied bythe upper die 10 is large, the slide motion controller 50 controls thepress molding force so that it is small. By doing so, the stress appliedto the metal plate W at the vertical wall part of the lower die 20 canbe reduced, thereby making it possible to effectively prevent the metalplate W from cracking at the vertical wall part.

(3) Third Embodiment

A configuration of a press molding apparatus 3 according to a thirdembodiment will be described with reference to FIG. 7. FIG. 7 is a viewshowing a configuration example of the press molding apparatus 3according to the third embodiment.

As shown in FIG. 7, the press molding apparatus 3 according to the thirdembodiment differs from the press molding apparatus 1 according to thefirst embodiment in that the press molding apparatus 3 includes an upperdie 11 and a lower die 21 instead of the upper die 10 and the lower die20, includes die cushions 44 and 45 instead of the die cushions 42 and43, and further includes members 46 and 47, an actuator controller 90,and actuators 91 to 95 in addition to the components included in thepress molding apparatus 1 according to the first embodiment. Theconfigurations of the third embodiment other than the componentsdescribed above are the same as those of the first embodiment.

The upper die 11 and the lower die 21 differ from the upper die 10 andthe lower die 20 according to the first embodiment in that a projectionis formed at a center on an upper surface side of the lower die 21, anda recess, corresponding to the projection of the lower die 21, is formedat a center on a lower surface side of the upper die 11.

The die cushions 44 and 45 differ from the die cushions 42 and 43according to the first embodiment in that the die cushions 44 and 45 areprovided on the upper die 11 side. In the third embodiment, the members46 and 47 provided on the lower die 21 side are elevated and lowered inaccordance with the operation for elevating and lowering the die cushionmain body 41. The die cushion 44 sandwiches and holds the metal plate Wwith the lower die 21 in the vertical direction, while the die cushion45 sandwiches and holds the metal plate W with the member 47 in thevertical direction. Further, in the third embodiment, the lower die 21is also elevated and lowered in accordance with the operation forelevating and lowering the die cushion main body 41.

The actuator 91 is disposed inside the upper die 11. The actuator 91changes the die shape of the upper die 11 in a direction to expand orcontract it in the horizontal direction of the drawing. The actuator 92is disposed outside the upper die 11. The actuator 92 changes the dieshape of the upper die 11 in a direction to expand or contract it in thehorizontal direction of the drawing.

The actuator 93 is disposed inside the lower die 21. The actuator 93changes the die shape of the lower die 21 in a direction to expand orcontract in the horizontal direction of the drawing. The actuator 94 isdisposed outside the lower die 21. The actuator 94 changes the die shapeof the lower die 21 in the direction to expand or contract in thehorizontal direction of the drawing.

The actuator controller 90 determines the press position of the metalplate W based on the operation for elevating and lowering the slide 30(the upper die 10) controlled by the slide motion controller 50, andcontrols the actuators 91 to 95 based on the press position of the metalplate W.

For example, the slide motion controller 50 controls the actuator 91,92, 93, and 94 so that the die shapes of the upper die 11 and the lowerdie 21 contract in the horizontal direction of the drawing as the pressposition of the metal plate W is gradually lowered.

As described above, in the third embodiment, not only the blank holdingforce exerted by the die cushions 44 and 45 can be controlled, but alsothe die shapes of the upper die 11 and the lower die 21 can becontrolled based on the operation for elevating and lowering the slide30 (the upper die 10).

Note that the present disclosure is not limited to the above-describedembodiments, and can be appropriately changed without departing from thespirit of the present disclosure. For example, although the second andthird embodiments have been separately described, the second and thirdembodiments may be combined.

From the disclosure thus described, it will be obvious that theembodiments of the disclosure may be varied in many ways. Suchvariations are not to be regarded as a departure from the spirit andscope of the disclosure, and all such modifications as would be obviousto one skilled in the art are intended for inclusion within the scope ofthe following claims.

What is claimed is:
 1. A press molding method for press-molding aworkpiece by a press die composed of an upper die and a lower die whileholding the workpiece by a die cushion, the press molding methodcomprising pressing process, in which a press position at which theworkpiece is pressed by the press die is gradually lowered whilerepeatedly pressing and releasing the workpiece by the press die aplurality of times until the press position reaches a bottom deadcenter, wherein in the pressing process, a holding force for holding theworkpiece by the die cushion is controlled separately from a pressmolding force for press-molding the workpiece by the press die.
 2. Thepress molding method according to claim 1, wherein in the pressingprocess, holding and releasing of the workpiece by the die cushion arerepeated a plurality of times.
 3. The press molding method according toclaim 2, wherein when the workpiece is released from the die cushion, ina predetermined number of times of the releasing out of a plurality oftimes of the releasing, the workpiece is in contact with both of thepress die and the die cushion, and in a remaining number of times of thereleasing out of the plurality of times of the releasing, the workpieceis separated from at least one of the press die and the die cushion. 4.The press molding method according to claim 1, wherein in the pressingprocess, at least one of an equipment state of a press moldingapparatus, a material state of the workpiece, and a die state of thepress die is monitored, and the press molding force is controlled basedon at least one of the equipment state of the press molding apparatus,the material state of the workpiece, and the die state of the press die.5. The press molding method according to claim 1, wherein in thepressing process, a die shape of the upper die and a die shape of thelower die are changed based on the press position.
 6. A press moldingapparatus comprising a press die composed of an upper die and a lowerdie and a die cushion, configured to press-mold a workpiece by the pressdie while holding the workpiece by the die cushion, and configured toexecute pressing process, in which a press position at which theworkpiece is pressed by the press die is gradually lowered whilerepeatedly pressing and releasing the workpiece by the press die aplurality of times until the press position reaches a bottom deadcenter, the press molding apparatus comprising: a first control unitconfigured to control, in the pressing process, a press molding forcefor press-molding the workpiece by the press die; and a second controlunit configured to control, in the pressing process, a holding force forholding the workpiece by the die cushion separately from the pressmolding force controlled by the first control unit.